Doc: Compress PNG images.

[Fdawgs]

Motivation / Problem

Repo size can always be smaller!

Description

Losslessly compress documentation PNG images using Pngcrush to reduce the repo size by a few bytes.

Limitations

N/A

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[LordAro]

This needs to be done extremely carefully, as PNG compressors tend to fiddle around with image palettes, and OTTD/grfcodec/etc is very specific about the image palette of the image - changing that will cause issues

Also, there's a conflict - which raises the other issue - as soon as this images get edited, the compression will get undone, and so will only serve to bloat the repo size.

Compressing the images in docs is fine though

[Fdawgs]

This needs to be done extremely carefully, as PNG compressors tend to fiddle around with image palettes, and OTTD/grfcodec/etc is very specific about the image palette of the image - changing that will cause issues

Thanks @LordAro, will update the PR to only update the doc images in that case.

[FLHerne]

Does this decrease the repo size? The old versions of the files are still in the history.

git clone by default copies the entire repository including all previous commits, so now most people are downloading both the old and new versions of the files (or one and a binary diff) resulting in an increase. Similarly, everyone with an existing clone will have to download the new versions when they git pull.

The only benefit is to users making a shallow clone with git clone --depth=n which is relatively unusual.

[Fdawgs]

Good point @FLHerne, will drop this PR. Thanks!